The present invention concerns improvements relating to interfacing optical transmission structures and more particularly, though not exclusively, to a method and an apparatus for coupling a first optical transmission means, such as an optical fiber, embedded within a composite such as an aircraft panel to a second optical transmission means, such as an optical fiber, external to the composite. The present invention also concerns such a method or apparatus which can provide a coupling to a minimal number of steps thereby simplifying the coupling procedure.
The phrase ‘embedded within a composite’ in the context of the present invention is intended to mean that, at a possible point of connection, the article is completely surrounded by the composite and is located beneath the exterior surfaces of the composite after manufacture. Such an embedded article is not exposed to the exterior surface and can only be accessed by entering the interior of the composite.
The term ‘composite’ as used herein is to be construed broadly, in that it is directed to any support structure for carrying a light transmission means. Typical composites are aircraft panels, and other supportive structures made from plastics materials, carbon fiber, glass or metal for example and include multi-layer structures.
The use of optical fibers and advanced composites is becoming more accepted in the aircraft industry over the previous systems of lightweight metals and electrical wiring. There are many advantages to the use of optical fibers, such as reduced weight, elimination of electromagnetic problems, such as noise pick up and incidental radiation of signals, lower raw material costs, and elimination of potential dangerous conductive paths. Whilst these advantages are clearly desirable, the use of optical systems in aircraft has its own specific characteristics, different from those associated with conventional systems, which have to date slowed acceptance of this new technology.
Fiber optics embedded in composite structures can provide elegant distributed and embedded sensing functions (e.g., of strain, temperature) as well as the potential for embedded communications links. Despite the proven functionality of such embedded optical fiber structures, problems remain as to the best way of interfacing (i.e., launching and extracting light) to/from the embedded optical fibers. One way, described in U.S. Pat. No. 5,299,273, involves attaching a relatively large optical connector to a composite laminate part having an optical fiber embedded therein. The optical connector is attached by trimming the structure across the path of the optical fiber thereby exposing an end of the fiber that lies flush with the surface of the structure. Then the optical fiber is polished and the connector is fitted using micro-positioning techniques to correctly align the connector and optical fiber.
Other current solutions include allowing delicate embedded fibers to emerge from the structure surface or edge (so called ‘flying leads’), or embedding fibers connectors in a surface of the composite at the ends or sides of embedded optical fibers for subsequent connection to external optical devices or other optical fibers. Examples of the latter type of coupling are shown in U.S. Pat. No. 5,809,197 and in the paper by S. Meller, J. Greene, C. Kozikowski, K. Murphy, R. Claus, “Polymer and Metal-Matrix Composite-Embedded Optical Fibres for Avionics Communications Links”, SPIE Proceedings Vol. 3042, pp. 383–388, 1997.
The provision of ‘flying leads’ is problematical in that these are potential single points of failure during use of the composite. As well as being prone to damage, the fibers muse be managed during composite manufacture (lay-up) which will increase manufacturing complexity, time and cost. Likewise, the provision of conventional embedded connectors at the composite surface can also complicate the manufacturing process particularly since these embedded connectors tend to be rather bulky and require careful protection. Additionally, resin accretion can occur round these connectors (and also in the case of flying leads) which can lead to embrittlement and contamination effects.
Generally, all of the above methods suffer from the problems of potential damage to the optical fibers emerging out of the composite and to be embedded connectors present at the surface of the composite when the composite needs to be ‘finished’ in its manufacturing process. These problems have hindered the universal acceptance of embedded optical fibers systems within the aircraft industry.
It is desired to overcome or at least substantially reduce the above described problems.